This invention relates to a raster centering circuit for a deflection system such as in a television receiver.
Frequently, relative misalignment of the components comprising a television display system such as the picture tube envelope, electron gun assembly and the deflection yoke cause the scanned raster to be not centered on the viewing screen. Generally, two alternatives are available to compensate for this condition. First, the raster may be enlarged by increasing the peak power of the deflection current to create an overscan condition. With an overscan condition, relatively small offset conditions of the raster will not be noticed as the entire viewing screen displays a picture. The main disadvantage of utilizing overscan to correct a centering problem is the additional power consumption by the deflection circuit and its components. In effect, any overscan represents a waste of power in that the overscan portion of the raster is not viewable.
The second alternative is to provide means for centering the raster by applying a direct current through the vertical or horizontal or both of the deflection windings to thereby shift the raster as is well-known in the art. Obviously, the least complex and least energy consuming arrangement for providing a D.C. centering current is desirable in any particular deflection circuit configuration.